Answer:
Jae should do nothing and continue purchasing the same amount of pens and pencils.
Step-by-step explanation:
The current rate of substitution that maximizes Jae's utility is Px / Py = 0.50 / 0.10 = 5. That means that Jae will purchase 5 pencils for every pen that he buys, and that is exactly what he is doing right now.